A drug-eluting stent is a device used in operations to treat coronary artery disease. It is usually inserted during balloon angioplasty, in patients who have suffered a heart attack or who have angina.
A coronary angioplasty procedure is performed to unblock coronary arteries that have become narrow due to fatty materials accumulating inside them. These narrowed vessels reduce the amount of blood and therefore oxygen that reaches the heart, which can cause chest pain (angina), as well as increasing the risk of myocardial infarction. Widening an affected artery enables blood to flow more easily and supply the heart muscle with enough oxygen.
During coronary angioplasty, a small balloon is inserted into an artery and inflated to open up the vessel. A stent is sometimes used to ensure the artery stays open. The stent, which is a small tube composed of wire mesh, enters the artery in a collapsed state, but when the balloon is inflated, the stent expands and presses against the artery walls. Once the balloon is removed, the stent stays in place, ensuring the artery is held open.
Two types of stent are available: the bare metal stent and the drug-eluting stent. The bare-metal stent acts as a scaffold that props the artery open. As the artery heals, tissue grows around the stent, which holds it in place. However, sometimes there is an excess growth of this scar tissue, which can lead to further blockage in the artery and re-narrowing (restenosis) of the vessel. Due to the risk of this complication, drug-eluting stents were developed, which are coated with a medication that is released over time to prevent this re-growth of the scar tissue. Research has shown that drug-eluting stents are not only as safe as bare metal stents, but reduce the restenosis rate by about half, when compared with the use of bare-metal stents.
Several different types of drug-eluting stent exist and the National Institute for Health and Care Excellence recommends that stents containing either sirolimus or paclitaxel are used, as these are the drugs that have been subjected to the most rigorous research.
The medications released from drug-eluting stents inhibit cell proliferation and activate signal transduction pathways. Consequently, although these stents are designed to prevent the proliferation and migration of vascular smooth muscle cells (factors that promote restenosis), they can also disrupt reendothelialization. This slows healing of the artery, as well as increasing the expression of tissue factors, which can lead to a prothrombogenic environment and the development of a clot inside the stent. This is referred to as stent thrombosis, a complication that is rarely seen with bare-metal stents. These clots can occur months or even years after the drug-eluting stent is implanted and can increase the risk of heart attack and death.
Patients are therefore prescribed anticoagulants (usually a combination of aspirin and ticlopidine or clopidogrel) to reduce the risk of clotting within the drug-eluting stent. However, researchers are not sure how long these medications need to be taken for, as it is not known how long the vessel takes to completely heal after the insertion of a stent. The long-term use of anticoagulants can also be an unappealing option for people with bleeding problems or those who require further surgery within a year of stent placement.
The Food and Drug Administration and the American Heart Association advise that medications such as clopidogrel are taken for at least a year after implantation of a drug-eluting stent. Cardiologists will advise patients on how long they should take anticoagulants or other medications for, depending on the type of blockage they had and their risk of bleeding. Patients who are likely to need further surgery within a year of stent implantation, may be advised that a bare-metal stent is a better option. Patients who are at an increased risk of bleeding or feel they will be unable to take anti-clotting medication may also be advised to opt for a bare-metal stent.
The use of drug-eluting stents has been successful in many people with heart problems, reducing the need for more invasive surgeries such as coronary artery bypass. Furthermore, the reduced rates of restenosis in patients who have a drug-eluting stent has significantly reduced the need for repeat angioplasty, which is associated with risks such as stroke and heart attack.